This study on relationships between immune response and structural genes coding for antibodies will utilize rabbits which produce high concentrations of antibody to the group-specific carbohydrates following immunization with streptococcal vaccines. Both the magnitude and homogeneity of this antibody response is under genetic control. Offspring of rabbits inbred for this trait will be bred to rabbits having different allotype combinations. Measurements of allotypic markers on the antibodies produced in the immunized F1 (heterozygous) generation as well as the subsequent homozygous generations will provide information on allotypic preference in the antibody response. Immunization of rabbits showing allotypic preference with a second antigen will provide further information on this relationship. The idiotypic markers, which include the amino acid sequences unique to the antibody binding site, appear to be inherited. Idiotypic and allotypic markers will be followed through several generations of rabbit families to ascertain whether obligatory associations exist between idiotypes and any of the allotypes or allotypic combinations. The rabbit is well suited for studies on relationship between allotypic and idiotypic markers because of the presence of heavy chain variable region allotypes.